Shockproof electrical resistor



E. AF. SEAMAN SHOCK PROOF ELECTRICAL RESISTOR yApril 2, 1946.

Filed March 11,' 1944 FIGURE l F IGURE 2 FIGURE 3 INVENTOR ELswonT; FSEAM N //\TTO NEY Patented Apr. 2, 1946 2,397,568 SHOCKPROOF ELECTRICALRESISTOR Ellsworth F. Seaman, Washington, D. C. Application March 11,1944, Serial No. 526,105

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370O. G. 757) 7 Claims.

My invention relates generally to resistors, and particularly toanimproved type of resistor which is greatly resistant to both mechanicaland thermal shock.

In some electrical installations, as aboard warships, aircraft, etc.where all equipment is subjected to tremendous shocks during battleconditions, and to severe vibration for long periods` failure ofelectrical resistor elements has rendered equipment useless.

I have invented an improved construction utilizing a metal supportingtube for the resistance wire in conjunction with certain of the hightemperature insulations, whereby it is possible to use these insulationsboth as a mechanical spacer element and as electrical insulatingmaterial, in order that the electrical function of the resistor may beadequately accomplished under conditions of high impact shock andvibration, as encountered aboard Warships or aircraft, etc.

It is the primary purpose of this invention to provide an improvedelectrical resistor which has greatly improved characteristics ofmechanical and thermal shock resistance and ruggedness.

Other objects will appear as the description progresses, and inconnection with the accompanying drawing in which:

Fig. 1 is a top or end view of a resistor illustrating one embodiment ofmy invention;

Fig. 2 is a side elevation, half in cross-section, of the resistor ofFig. 1;

Fig. 3 is an enlarged view of a portion of the sectioned part of Fig. 2.

The resistor comprises a metal base 4 in the form of a cylindrical tube,although it is to be understood that the tube may have any othersuitable cross-sectional form, as that of an oval, etc., and its axismay be curved. Preferably, the tubular base 4 should be of aluminum,although any suitable metal such as copper having a high thermalconductivity and resistance to shock and fatigue may be used. Ceramicmaterials are particularly unsuitable for the base because of their lowshock resistance. The exterior of the tube is covered with anonhygroscopic, iiexible high temperature resistant insulation material5. I have found that one particularly suitable insulation for thepurpose of this invention is a layer of asbestos or glass tapeimpregnated with a silicone resin. Alternately the base may be coveredwith a material having exceptionally high heat resistance such as POLY F1114" which is a polymer-ized tetrauoroethylene. This will withstandhigher temperatures than the silicone resins and will not crack.

The resistance wire 6 which is wound on the base 4 over the insulation5. is iirst covered With an insulating material l which is substantiallyunaiected by high temperature. The insulation 'l may be either acovering of ber glass impregnated with silicone resin, or it may be theexceptionally high heat resistant insulating material POLY F 1114.

The insulation covered wire 6 is closely wound in one or more layers onthe base as shown in the drawing wherein two layers are provided. Asshown, the iirst layer terminates adjacent the end of the base, and thesecond layer is a continuation of and is closely wound over the firstlayer, terminating adjacent the beginning of the first layer. The endsof the Wire are electrically connected to binding posts 8 and 9respectively, these posts being electrically insulated from the metalbase 4 as by insulating bushings I0 and Il.

In order to protect the resistor unit from the eiects of -moisture andfrom abrasion, it is covered by an exterior protective sheath or filmI2. This sheath may be a sprayed layer of copper which is subsequentlysoft-annealed to remove brittleness. Instead of the copper spray, thesheath may comprise metal foil wrapped around the outside of the wireand bound with glass twine or the like. I1' the temperature of thecompleted resistor is to be low enough so that the heat radiatingcapacity of thesheath is not important, the sheath may be an insulatingmaterial. In this case it should be one such as the POLY F 1114 whichwill not crack due to temperature or other drying conditions. f

Where the resistor is of the variable type and the wire 6 is bare forcontact with a wiper or contact arm, the wire is wound on the insulation5 with its turns spaced. The spaces between the turns of wire may thenbe filled with an insulating spacer which may comprise strings or thelike of ber glass or the like, impregnated win..l silicone resin or POLYF 1114.

Neither the form of the terminals shown, nor the means for mounting theresistor are a part of this invention.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

I claim:

1. An electrical resistor comprising a tubular metal base having a highresistance to shock and fatigue; an insulating covering over theexterior of said base, said covering being substantially unailected byhigh temperatures; a resistance wire wound over said covering and aroundsaid base, the turns of said resistance wire being covered with aninsulation material substantially unaffected byhigh temperature; and anexterior moisture proof sheath over said resistance'wire, said exteriorsheath comprising a polymerized tetrailuoroethylene.

2. An electrical resistor comprising a tubular metal base having a highresistance to shock and fatigue; an insulating covering over theexteriorof said base, said covering being substantially unail'ected byhigh temperatures, said insulating covering comprising nbre glassimpregnated with a silicone resin; a resistance wire wound over saidcovering and around said base, the turns of said resistance Wire beingcovered with an insulation material substantially unaffected by hightemperature; and an exterior moisture proof sheath over said resistancewire.

3. An electrical resistor comprising a tubular metal base having a highresistance to shock and fatigue; an insulating covering over theexterior oi' said base, said covering being substan tially unaffected byhigh temperatures, said insulating covering comprising a polymerizedtetraiiuoroethylene; a resistance wire wound over said covering andaround said base, the turns of said resistance wire being covered withan insulation material substantially unaffected byhigh' temperature; andan exterior moisture proof sheath over said resistance wire.

4. An electrical resistor comprising a tubular metal base having a highresistance to shock and fatigue; an insulating covering over theexterior oi' said base, said covering being substantially unaiected byhigh temperatures: a resistance wire wound over said covering 4andaround said base, the turns of said resistance wire being covered withan insulation material substantially unaffected by high temperature,said insulation material comprising fiber glass impregnated with asilicone resin; and an exterior moisture proof sheath over saidresistance wire.

5. An electrical resistor comprising a tubular metal base having a highresistance to shock and fatigue; an insulating covering over theexterior of said base, said covering being substantially unaffected byhigh temperatures; resistance wire wound over said covering and aroundsaid base, the turns of said resistance wire being covered with aninsulation material substantially unaffected by high temperature. saidinsulation material comprising a polymerized tetraf ance Wire, saidexterior sheath, said insulating lcovering on said base, and saidinsulation material on said wire each comprising a polymerizedtetraiiuoroethylene.

'7.` An electrical resistor comprising a tubular metal base having ahigh resistance to shock and fatigue; an insulating covering over theexterior of said base, said covering being substantially unaffected byhigh temperatures; a resistance wire wound over said covering and aroundsaid base, the turns of said resistance Wire being covered with aninsulation material substantially unaiected by highvtemperature, saidinsulating covering on said base and said insulation material on saidwire each comprising fiber glass impregnated with a silicone resin; andan exterior moisture proof sheath over said resistance wire.

ELLSWORTH F. SEAMAN.

